Upon the approach of any ambulance, police or fire department vehicle, or upon the approach of Triborough Bridge and Tunnel Authority vehicles giving adequate warning by means of bell or warning light, all traffic shall proceed as near as possible to the right-hand curb on the roadway and stop, unless and until otherwise directed by an employee of the Triborough Bridge and Tunnel Authority, properly identified, or a New York City police officer, or until such traffic shall have passed.